What diagnostic test, such as a computed tomography (CT) scan, is recommended for a patient with unilateral hearing loss?

Diagnostic Imaging for Unilateral Hearing Loss

For unilateral hearing loss, MRI of the head and internal auditory canal is the imaging modality of choice, as it is superior for detecting the soft-tissue abnormalities (such as vestibular schwannomas, labyrinthitis, and cochlear nerve pathology) that most commonly cause sensorineural hearing loss. 1

Critical First Step: Determine Type of Hearing Loss

The appropriate imaging depends entirely on whether the hearing loss is conductive versus sensorineural:

• Clinical examination with tuning fork tests (Weber and Rinne) and audiometry must be performed first to differentiate the type of hearing loss 1
• This distinction fundamentally changes the imaging approach and cannot be bypassed 1

For Sensorineural Hearing Loss (Most Common in Unilateral Cases)

MRI is the definitive first-line imaging modality for the following reasons:

• MRI with dedicated internal auditory canal (IAC) protocol using thin sections is highly sensitive for detecting vestibular schwannomas, the most critical diagnosis not to miss in unilateral sensorineural hearing loss 1
• MRI can identify neoplasms within the cochlear labyrinth or IAC, inflammatory changes (labyrinthitis, neuritis), hemorrhage, and abnormalities along the auditory pathways 1
• CT temporal bone is insensitive for soft-tissue abnormalities that commonly cause sensorineural hearing loss and cannot adequately visualize intralabyrinthine or intracanalicular enhancement 1
• Contrast-enhanced head CT is significantly less sensitive than MRI for detecting tumors like vestibular schwannomas 1

MRI Technical Specifications

• Use dedicated IAC protocol with thin sections across the IAC and inner ear 1
• High-resolution 3-D T2-weighted images provide submillimeter assessment and are highly sensitive 1
• IV contrast administration may facilitate visualization of inflammatory changes and neoplasms, though there is insufficient evidence proving incremental benefit beyond non-contrast MRI IAC protocol 1

When CT May Have Limited Utility in Sensorineural Loss

• CT temporal bone may show indirect clues such as labyrinthine ossification from prior infection or bony remodeling of the IAC suggesting vestibular schwannoma 1
• In post-traumatic sensorineural hearing loss specifically, CT can demonstrate fractures extending across the otic capsule 1
• However, CT should not replace MRI as the primary imaging modality for sensorineural hearing loss 1

For Conductive Hearing Loss

CT temporal bone without IV contrast is the first-line imaging modality in this scenario:

• CT provides excellent delineation of the external auditory canal, ossicular chain, and bony labyrinth 1
• CT identifies otosclerosis, ossicular erosion or fusion, round window occlusion, and superior semicircular canal dehiscence 1
• Bone algorithm reconstructions are essential to maximize visualization of middle ear structures 1
• IV contrast is not beneficial for temporal bone evaluation in conductive hearing loss due to the density of surrounding bone 1
• Standard head CT has no role and lacks the necessary resolution 1

Special Considerations in Pediatric Unilateral Hearing Loss

Both CT temporal bone and MRI may be necessary in children with unilateral or asymmetric sensorineural hearing loss:

• Inner ear malformations are detected in 28.9-41% of children with unilateral sensorineural hearing loss on CT 2, 3
• When both modalities are obtained, 31% of cases show clinically significant abnormalities on only one modality 3
• CT detects bony malformations (Mondini deformity, enlarged vestibular aqueduct, narrow internal auditory canal) that MRI may miss 2, 3
• MRI detects soft tissue and neural abnormalities that CT cannot visualize 3
• Bilateral malformations are found in 19.4% of cases initially presenting as unilateral hearing loss, making imaging critical for genetic counseling and contralateral ear monitoring 2

Pediatric Follow-up Requirements

• Progressive hearing loss occurs in 6.1% of children with unilateral sensorineural hearing loss, including 14.8% of those with nonprofound loss and normal CT 2
• Longitudinal audiologic assessment of both ears is mandatory regardless of imaging findings 2

Common Pitfalls to Avoid

• Do not order standard head CT for hearing loss evaluation—it lacks the resolution needed for temporal bone structures 1
• Do not use CT angiography (CTA) or MR angiography (MRA) for initial workup of isolated hearing loss 1
• Do not assume CT temporal bone is adequate for sensorineural hearing loss—you will miss vestibular schwannomas and other soft tissue pathology 1
• Do not skip audiometry—imaging selection is impossible without knowing the type of hearing loss 1